Visual Agnosia and Higher- Order Thought Theory

A slight modificationMy own view is that, when one has a firstorderconscious state, the HOT is better viewedas intrinsic to the overall conscious state, so thatwe have a complex conscious state with parts.Conscious mental states are then bestunderstood as global brain states which arecombinations of passively received perceptualinput and presupposed higher-order conceptualactivity directed at that input. Concepts in themeta-psychological thoughts are thuspresupposed in having first-order consciousstates.

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More on Associative Visual Agnosia• Difficulty on naming tasks and grouping objectstogether.• Normal recognition of objects through modalitiesother than vision, e.g. by touching the object.• Intact basic visual perception, e.g. patients cancopy objects or drawings that they cannotrecognize.• Patients will often see the details or parts of anobject, but not the “whole” of an object at aglance.

A Problem for HOT Theory• It thus seems possible to have aconscious experience of an object (albeit,an abnormal experience) in the absenceof higher-order conceptualization of theincoming visual information.• There is a first-order perception of anobject without the accompanying conceptof that object. Thus, its “meaning” is goneand the object is not recognized.

HOT theory and associative agnosia: A reply• It should first be noted that, if HOT theory is true,there must be some HOT for there to be aconscious state at all. So a HOT theorist canstill hold that some other HOT is present in suchabnormal cases, which reflects the way that thepatient is experiencing the object (e.g. a whistleor paintbrush). For example, if a patientexperiences object O (mistakenly) as someother object O’, then the HOT would have the O’concept in it. If they experience object O only bycertain parts or fragments, then those conceptswill be in the relevant HOT. Thus, no problemso far. There is no reason to suppose that theseHOTs are entirely absent in such cases.

REPLY (cont.)• It is also important to recognize that associativeagnosics still do have the relevant correctconcept because the evidence shows thatpatients can apply it to other modalities (e.g.touch, hearing). For example, identifying awhistle by sound but not by sight. The problemis simply that, in cases of vision, the mechanismby which the appropriate concept is triggered isclearly defective. So while one might be said tobe having a conscious visual perception of awhistle in some sense, the patient is notexperiencing the object as a whistle.

It is helpful to view this in light of another objection to HO theory:The problem of misrepresentation: An important objection toHO approaches is the question of just how such theories canexplain cases where the HO state might misrepresent thelower-order (LO) mental state (Levine 2001). If we are dealingwith a representational relation between two states, it seemspossible for misrepresentation or malfunction to occur. If itdoes, then what explanation can be offered by the HO theorist?If my LO state registers a red percept and my HO stateregisters a thought about something green due, say, to someneural misfiring, then what happens? It seems that problemsloom for any answer from a HO theorist and the cause of theproblem has to do with the very nature of the HO theorist’sbelief that there is a representational relation between the LOand HO states. For example, if the HO theorist takes the optionthat the resulting conscious experience is reddish, then itseems that the HO state plays no role in determining thequalitative character of the experience.

This is an objection that must be takenseriously and it forces HO theorists to beclearer about just how to view therelationship between the LO and HOstates. One possible reply to thisobjection is to construe the LO and HO aspart of the same integrated global state,so that misrepresentation arguably cannotoccur. That is, a coherent and accurateconscious state only occurs when the LOand HO concepts match.

Associative Agnosia and MisrepresentationThe visual agnosic consciously perceives things, but cannotrecognize what they are. They often mistake one object for another;for example, even mistaking one’s wife for a hat (Sacks, 1987). Thisdiffers from Levine’s case in that we are referring to the perceptionof objects as opposed to color perception. Visual agnosics are alsonot blind and do not have damage to the relevant areas of the visualcortex (contrast this with blindsight). However, a HOT theorist mightview this as an unusual case where the typical HOT does not“match up” with the first-order visual input. Thus, it seemsreasonable to view associative agnosia as a case where the “normal”concept in the HOT does not accompany the input received throughthe visual modality. So, as was mentioned earlier, associativeagnosia would be a case where the LO state registers a percept ofan object O, but the HO state (mistakenly) associates a concept ofO’ with LO. Bare visual perception remains but is confused andloses meaning due to the lack of a matching concept, resulting in adifferent and rather confusing phenomenological experience.

Integrative Agnosia• From Riddoch and Humphreys (1987)• A common and more specific kind of associativeagnosia• In light of the misrepresentation issue, perhapswe can also sometimes understand associativeagnosia more specifically as a problem of the“impaired integration of local shape parts intohigher-order shapes.” (Farah 2004, p. 78)• Agnosics often mistakenly guess at the identityof an object (e.g. calling a baby carriage a“bicycle”) on the basis of a single feature (e.g.wheels)

Integrative Agnosia (cont.)• This has suggested to many that there is a “hierarchicalsystem of shape representation, whose lower-level partrepresentations are relatively intact but whose higherlevelintegration of the parts is damaged…” (Farah 2004,p. 78)• Relative to HOT theory, this also suggests that it is bestto hold that it takes the integration of both the LO stateand the HOT to produce a coherent and accurate visualexperience of an object. Otherwise, a loss of “global” or“gestalt” perception occurs. But this is not a problem forHOT theory as such; if anything, HOT theory can neatlyexplain what has gone wrong.

ConclusionAssociative agnosia can actually be neatlyexplained by HOT theory, rather thanbeing a serious difficulty for the theory.Such cases reinforce the explanatorypower of HOT theory in terms of theimportance of matching HO concepts toLO input. These cases also show theadvantage of understanding normal visualperception as genuine integrations of LOand HO states.

References• Gennaro, R.J. 1996. Consciousness and Self-consciousness: A Defense ofthe Higher-Order Thought Theory of Consciousness. Amsterdam &Philadelphia: John Benjamins.• Gennaro, R.J. 2004. “Higher-order thoughts, animal consciousness, andmisrepresentation: A reply to Carruthers and Levine.” In Gennaro 2004a.• Gennaro, R.J., ed. 2004a. Higher-Order Theories of Consciousness: AnAnthology. Amsterdam and Philadelphia: John Benjamins.• Farah, M. 2004. Visual Agnosia, second ed. Cambridge, MA: MIT Press.• Levine, J. 2001. Purple Haze: The Puzzle of Conscious Experience.Cambridge, MA: MIT Press.• Riddoch, M.J. & Humphreys, G.W. 1987. A case of integrative visualagnosia. Brain, 110, 1431-1462.• Rosenthal, D.M. 2005. Consciousness and Mind. Oxford University Press.• Sacks, O. 1987. The Man who Mistook His Wife for a Hat. New York:Harper & Row.• Teuber, H.L. 1968. Alteration of perception and memory in man. In L.Weiskrantz ed. Analysis of Behavioral Change. New York: Harper & Row.